1. Field of the Invention
The present invention relates to a device for passively tracking individuals. More specifically, the present invention is directed to a device for recording the movement of individuals using GPS signals for later comparison with event data to determine if the individual was in the vicinity of the event within a given time frame.
2. Discussion of Background Information
Devices and methods for monitoring the movements of individuals are known. One example is a two-piece tracking unit that includes a tag attached to a limb of a wearer (e.g., on the wrist) tethered to a large suitcase or body-worn unit that carries batteries and associated circuitry. This device is an “active” system in that it compares its position with certain ongoing restrictions to detect violations (e.g., a parolee enters a restricted area, such as a bar). The requirements of this type of active system dictate the large size and weight of this system. The associated manufacturing and operating costs have limited the commercial viability of these devices, such that it is believed that less than 1500 units are in actual use in the United States.
Smaller one-piece wearable units have been suggested, such as in U.S. Pat. No. 5,867,103 to Taylor and PCT/US00/16092 to Layson. Both disclose a self-contained device that can be worn around an individual's limb. The devices include standard GPS receiving circuitry, a memory, a power source, and some methodology to download the contents of the memory to a remote station for comparison with other data, typically crime data.
A drawback of the Taylor device is that it fails to account for the power supply and management system necessary to make these devices commercially viable. Specifically, the power requirements of the Taylor device would only allow for short-term use based on available battery technology. Layson addresses this problem with various battery recharging schemes such as solar cells and high-speed inductive transfer. However, these procedures are not believed to be commercially viable. It is believed that efforts to solve these problems have focused on improved batteries and lower power consumption methodologies that would provide extensive use (on the order of thirty days) between recharges. To date, this approach has not proved successful.
A need therefore exists for a relatively small wearable tracking unit and associated methodology with a high commercial viability.
The above noted prior art devices produce location data that reflect a user's location over time. This location data can be compared with incident data, such as crime data, to determine whether the user was in the area at the time of the incident. The noted Layson application contemplates that a database of several crime incidents can be compared with a database of movement of multiple users to identify instances of overlap. However, this type of comparison of raw databases would tax current computer limitations and be slow to produce results. Swifter analysis is preferable in these matters (if for no other reason than to minimize opportunity for criminal flight).